In early computer systems, the construction comprised a mainframe computer and a series of terminals connected to the mainframe. The terminals had little or no processing power.
Over a period of time the nature of computer systems has changed. The mainframe has been replaced by a series of individual computers connected together in a network. In an office environment each individual computer can be a personal computer which is also called a desktop computer.
In the fire detection industry the personal computers of an office network are replaced by so-called panels each of which has computing power and which are connected together in a network. The panels “talk” to one another and to the fire detectors which are connected to them.
In all networks, the requisite network integrity is lost should a cable be damaged, resulting in an open circuit, or should the network be shorted out. In an office environment this is more of an inconvenience than a major problem. Some unsaved data may be lost but usually any problems which have arisen can be rectified without there being long term effects. However, when the network is that of a fire detection system the consequences of the system being down for any period of time can be catastrophic.
Networks which are “self healing” have been proposed. Simply by way of example a system is known in which each node on a ring only “speaks” to its neighbour. If a host has any data which it needs to transmit, the data is loaded onto the controlling inter-node protocol. The data is then passed from node to node until all the nodes on the ring have received the data. The nodes continuously “handshake” with each other and, in the event of a fault which prevents data being transmitted along a specific route, an alternative route is arranged by the protocol.
The present invention seeks to provide an improved network based on the RS-485 protocol and which is capable of recovering from open and short circuits thereby to restore network integrity.